Separate external display tasks in Overview

- Sort external display tasks into front of Overview to create its own sections, all external display tasks are treated as large tile
- Fixed expected position of currentPage and runningTask respectively
- Fixed Desktop and fullscreen TaskView to launch with displayId from its first available task

Bug: 391311008
Flag: com.android.launcher3.enable_separate_external_display_tasks
Test: RecentTasksListTest
Change-Id: Ida0ccab00d3e4d74513812a11241dfc908bde991